The present invention relates to a power supply circuit, a driving device, an electro-optic device, an electronic apparatus, and a method of supplying driving voltages.
In a simple-matrix type liquid crystal panel (an electro-optic device, in a broad sense), improvement in the response speed is attempted with a multi-line (Multi Line Selection, hereinafter abbreviated to MLS) driving method of simultaneously selecting a plurality of common electrodes (scanning electrodes, in a broad sense), and increasing in contrast and reduction in power consumption are attempted.
In this MLS driving method, an interval of selection period, in which a selection voltage is applied to a common electrode in one frame period, is narrowed and on the other hand, the same common electrode is selected a plurality of times in one frame period. Accordingly, the selection voltage of the common electrode can be lowered, and an average transmissivity of pixels can be improved, thus improving contrast of a liquid crystal panel. For this reason, the driving voltage for segment electrodes (signal electrodes, in a broad sense) is determined corresponding to a scanning pattern (an applied pattern, a selection pattern) of the selection voltage of common electrodes to be simultaneously selected. Then, turned on or off of a pixel is controlled by an effective voltage applied to the liquid crystal device in one frame period.
In the case where a simple-matrix type liquid crystal panel is driven with the MLS driving method of simultaneously selecting four lines of common electrodes, if a non-selection voltage for common electrodes and a center voltage VC for the driving voltage of segment electrodes are made in common, seven levels of voltages (V3, V2, V1, VC, MV1, MV2, MV3) will be required.
FIG. 18 shows a relationship of the seven levels of voltages in the case where the simple-matrix type liquid crystal panel is driven with the MLS driving method of simultaneously selecting four lines of common electrodes.
Here, the voltages V3 and MV3 are the selection voltages of the common electrode. The voltage VC is the non-selection voltage of the common electrode, and is the driving voltage for the segment electrode. The voltages V2, V1, MV1, and MV2 are the driving voltages for the segment electrode.
The voltage difference between the voltage V3 and the center voltage VC is denoted by v3, the voltage difference between the voltage V2 and the center voltage VC by v2, and the voltage difference between the voltage V1 and the center voltage VC by v1. At this time, the voltage difference between the center voltage VC and the voltage MV3 is v3, the voltage difference between the center voltage VC and the voltage MV2 is v2, and the voltage difference between the center voltage VC and the voltage MV1 is v1. Here, the voltage difference between the voltage V2 and the voltage V1 (=the voltage difference between the voltage MV1 and the voltage MV2) is equal to the voltage difference between the voltage V1 and the center voltage VC (=the voltage difference between the center voltage VC and the voltage MV1). International Patent Publication No. WO 97/22036 is an example of related art.
If the above-described driving voltages are applied to the segment electrode in an ideal waveform, the same display quality (the same density, for example) is obtained for any display pattern.
However, there is produced dullness in the voltage waveform applied to the liquid crystal device itself, due to the own load of the liquid crystal device, the wiring resistance, or the like. For this reason, the effective voltage applied to the liquid crystal device becomes different from the ideal voltage depending on display patterns, thus deteriorating the display quality.